The invention applies to an ac voltage clipper to be used in MOS-circuits with an ac power supply. In that case the ac voltage has to be rectified by a rectifier. To protect the rectifier against damage caused by ac over-voltages at its input, it is necessary to limit the ac voltage by a clipper, if said voltage exceeds a predetermined threshold. The clipper should especially be applied in circuits where an ac voltage of highly varying amplitude is provided e.g. in the case of a LC-resonator influenced by an ac magnetic field.